The generation and control of muscle contraction involves complicated interactions between actin and myosin and between actin and tropomyosin-troponin, respectively, as regulated by MgATP and Ca ion. This proposal deals with the novel use of chemical modification techniques to introduce covalent crosslinks between muscle protein subunits and to introduce fluorescence probes at a specific place in the sequence of a given muscle protein. Since each of the subunits of the muscle proteins (9-10 total) differ in molecular weight, subunit proximity information can be obtained by an analysis of the molecular weight distribution produced by mild and selective crosslinking conditions. The sensitive fluorescence properties of the probes can be used to obtain information about binding stoichiometry as well as conformational changes. These in vitro studies involving various combinations of the proteins known to interact as modulated by Ca ion and MgATP will provide a more detailed knowledge of the molecular interactions involved in muscle contraction.